This invention relates to a controlled regenerative d-c power supply for converting a-c energy, received from an a-c power system, to d-c power for delivery to a load, where at times power flows in the reverse direction from the load and through the d-c power supply back to the a-c power system. This invention also relates to a method of operating such a regenerative d-c power supply and, more particularly, to a method for controlling an output voltage of the d-c power supply which is fed to load.
A controlled regenerative d-c power supply is disclosed in U.S. Pat. No. 4,375,612. In that d-c power supply, a-c energy from an a-c power system is converted by a phase-controlled SCR rectifier bridge, which is followed by a series-connected filter choke and a shunt-connected filter capacitor, to d-c power for delivery to a load. A positive line of the d-c power supply, connected to a positive terminal of the rectifier bridge, includes the filter choke, as well as a first diode, while a negative line, connected to the negative terminal of the rectifier bridge, includes a second diode. The cathodes of the two diodes are connected to one another by a first controllable converter valve in the form of a silicon controlled rectifier, the anodes of the two diodes being coupled to one another by a second controllable converter valve also in the form of a silicon controlled rectifier.
To control the magnitude of the d-c output voltage of the d-c power supply when power is being transmitted to the load, a voltage regulator component compares a reference voltage with the actual d-c output voltage and generates in response to the comparison an error signal transmitted to a driver stage. The driver stage activates the thyristors of the rectifier bridge in response to the error signal from the voltage regulator component.
In a power supply in accordance with the disclosure of U.S. Pat. No. 4,375,612, the maximum d-c output voltage equals the d-c voltage of an uncontrolled rectifier. In order to return to the a-c power network energy generated in the load, the controllable converter valves are controlled by means of another driver stage in response to a signal from the voltage regulator component. This component detects, by monitoring the d-c output voltage, the direction in which energy in being transported. The amount of current flowing back into the a-c power network is varied by the rectifier under the control of the voltage regulator component. As energy is being returned to the a-c power network, the magnitude of the d-c output voltage is necessarily reduced. Because of this process, it may happen that the controlled rectifier fails to commutate via the a-c power network. This phenomenon is termed "inverter commutation failure."
An object of the present invention is to provide an improved regenerative d-c power supply of the above-described type.
Another object of the present invention is to provide a method for the improved operation of such a d-c power supply.
Another, particular, object of the present invention is to provide such a method and apparatus in which the likelihood of inverter commutation failure is decreased.
Yet another particular object of the present invention is to provide such a method and apparatus in which the d-c voltage available at the output of the d-c power supply is greater than the voltage of an uncontrolled rectifier.
A further object of the present invention is to provide such a method and apparatus which has an enhanced efficiency.